This invention relates in general to vehicle stability control systems and in particular to detection and correction of vehicle yaw movement while the vehicle is towing a trailer.
With the increasing popularity of recreational activities such as boating, snowmobiling and similar activities, the need to tow trailers for transporting recreational equipment is increasing. Additionally, many motorists have access to light utility trailers for hauling items. The increasing need to tow trailers has been noted and vehicle manufactures have responded by marketing pickup trucks and sport utility vehicles equipped with trailer towing packages that can include a trailer hitch, a wiring harness and connector for the trailer brake lights and additional cooling capacity for the engine coolant and lubricating oil. A typical vehicle 10 towing a trailer 12 is illustrated in FIG. 1. The towing vehicle 10 is equipped with a trailer hitch 14 that is connected to a trailer tongue 16 that extends from the front of the trailer 12. While a trailer 12 having two wheels is shown, trailers with four or more wheel, usually mounted upon multiple axles are also common. Typically, light trailers do not have trailer brakes and are dependent upon the towing vehicle brakes for slowing and stopping. However, heavier trailers, such as camper trailers are often equipped with electric or hydraulic brake systems.
Due to their nature, trailers are totally controlled by the towing vehicle. Outside factors, such as loading, speed, road conditions, cross winds and movement of the towing vehicle can induce unwanted motions in a trailer. Among such unwanted motions, is rotation, or yaw motion, as represented by the double headed arrow labeled 18 in FIG. 1, about a vertical axis 20 that passes through the center of gravity of the trailer 12. Such yaw motions tend to increase with speed and are transferred through the trailer tongue 16 and hitch 14 to the towing vehicle 10 where similar yaw motions, as represented by the double headed arrow labeled 22, may be induced about a vertical axis 24 passing through the center of gravity of the towing vehicle 10.
The yaw motions of the towing vehicle 10 can develop quite suddenly and, if the vehicle operator does not react quickly, and correctly, can result in loss of directional control of the towing vehicle. An improper response by the towing vehicle operator to trailer induced yaw motions can actually exacerbate the yaw motions. In an extreme situation, the combination of the trailer 12 and vehicle 10 may jackknife, run off the road, or cross into the opposing traffic lane. Any of these results are most unsatisfactory. Additionally, trailers are typically not equipped to detect yaw motion. Accordingly, it would be desirable to be able to detect the development of yaw motions in a towing vehicle sufficiently in advance of a directional stability problem developing to allow time for the vehicle operator to take corrective actions. It also would be desirable to provide such detection by utilizing components already present upon the towing vehicle. It would be further desirable to use brake control systems present upon the vehicle to correct the trailer induced towing vehicle yaw motions before directional control problems develop.